Automatic landing elevator system



Feb. 16, 1954 A. o. LUND 2,669,324

AUTOMATIC LANDING ELEVATOR SYSTEM Filed June 26, 1952 2 Sheets-Sheet lR9 FigJ. Am

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m? gag 8% R8 ATTORNEY 2 Sheets-Sheet 2 INVENTOR Feb. 16, 1954 A. o. LUNDAUTOMATIC LANDING ELEVATOR SYSTEM Filed June 26, 1952 Fig.|A.

Patented Feb. 16, 1954 UNITED STATES PATENT OFFICE 2,669,324 AUTOMATICLANDING ELEVATOR SYSTEM Alvin '0. Lund, Great Notch, N. J., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application June 26, 1952, Serial No. 295,705 18 Claims.(01. 18729) This invention relates to apparatus for con- Which it is tostop, the adjustment of the braktrol ing the position of a movable bodyand it ing efforts enables the elevator car to stop achas particularrelation to automatic landing curately at the desired point regardlessof the elevator systems wherein an elevator car is landed load carriedby the car. accurately at a floor regardless of the load car- It istherefore an object of the invention to ried by the elevator car.provide an improved system for controlling the In automatic landingelevator systems it is the position of a movable body.

practice to initiate a. stopping operation of a It is another object ofthe invention to provide moving body such as an elevator car at apredeimproved load-responsive braking apparatus for termined distancefrom a point at which the body a moving body.

is to stop. If the load represented by the body It is a further objectof the invention to proremains constant, accurate stopping operationsvide load-responsive mechanical and electrical may be obtained. However,if the load reprebraking for a movable body.

sented by the body is subject to variation, the It is also an object ofthe invention to provide body may undershoot or overshoot the point atan elevator system wherein load-responsive which it should stop Onesolution for trllS promechanical and electucal braking are initiated ablem W111 be found in my copending appl cation, predetermined distancefrom a point at WhlCn Serial No 206,407 filed January 1'7, 1851 now anelevator car is to stop.

Patent No. 2,641,337. It is an additional object of the invention toAlthough aspects of the invention are suitable 20 provide a controldevice for a variable load which for various types of moving bodies, theinvention includes a stepping switch responsive to the is particularlysuitable for elevator systems and magnitude of the load will bedescribed with reference to a moving body It is a still further objectof the invention to in the form of an elevator car. provide an elevatorsystem wherein the brakin In an elevator system both mechanical and ofan elevator car is controlled by the position of electrical braking havebeen employed. The a stepping switch which is responsive to themechanical brake conventionally is spring-apload carried by theelevator. plied and is released in response to energization Otherobjects of the invention Will be apparent of an electrical motor whichmay be in the form from the following description taken in conjuncof asolenoid operating on a magnetic armature. tion with the accompanyingdrawings in which: Dynamic braking is well understood in the art, Figure1 is a schematic view with circuits shown and may be employed not onlyfor direct-current in straight line form of an elevator system emmotorsbut for alternating-current motors such bodying the invention. asinduction motors to which direct current, for Fig. 1A is a keyrepresentation of electroexample, may be supplied for braking purposes.magnetic switches and relays employed in the In accordance with theinvention, the braking system of Fig. 1. If Figs. 1 and 1A are placed inof an elevator car is varied in accordance with horizontal alignment itwill be found that corthe loading of the car. Such variation may beresponding coils and contacts of the switches introduced in themechanical braking or in the and relays are substantially in horizontalalignelectrical braking, but in a preferred embodiment ment.

of the invention, the variation is introduced in Fig. 1B is a schematicview of a stepping switch both mechanical and electrical brakingefforts. employed in the system of Fig. 1.

In a preferred embodiment of the invention, a Fig 1C is a vector diagramillustrating certain load-responsive device measures the load carriedvoltage relationships in the system of Fig. l, and by an elevator. Inaddition, a source of energy 5 Fig. 2 is a view in elevation with partsscheis scanned to provide a variable output. The matically shown of aninductor relay employed scanning of the source may be effected by astepin the system of Fig. 1. ping switch which is responsive to thedifference The relays and switches employed in the elevabetween thequantity measured by the load-retor system of Fig. 1 may have break orback consponsive device and the output obtained from the tacts which areclosed when the relay or switch source of energy. Adjusting devices arethen is deenergized and dropped out. Each of the recontrolled by thestepping switch for the purpose lays and switches employed in the systemof Fig. of adjusting braking efforts of mechanical and 1 may have frontor make contacts which are electrical braking apparatus. If a stoppingoperclosed when the relay or switch is energized and ation of theelevator car is initiated at a predepicked up.

termined distance from, a point or floor from Each set of contacts of arelay or switch is make contacts M6 of justed in accordance with afunction of the loading of the motor I! for the the braking eifort as afunction of such loadings.

The car switch CS is shown vator car Ill, but in association withcircuits which are controlled by the car switch. It will be noted thatthe car switch normally occupies a stopping position wherein it connectsa contact CS2 to the bus L4. Such connection controls in part theenergization of a stop control relay S. The

through either make contacts M4 of the running relay or make contacts'IOTI of a first timing relay.

The car switch CS may be moved by the car attendant to an up positionwherein it connects a contact CS3 to the bus L4. In this position, thecar switch completes the following circuit: L4, CS, CS3, U, LUI, 22, M,L5. This circuit includes a limiting switch 22 which is normally closed,but which is cam operated to open as the car switch.

The car attendant also may operate the car switch to a down positionwherein the car switch connects a contact CSl to the bus L4. In thisposition the following circuit is completed: L4, CS, CSI, D, LDl, 23, M,L5. This circuit includes a limit switch 23 which is normally closedbuses L4 and L5 in series with the make contacts M5 of the running relayand the break contacts F3 and F4 of the inductor relay. Under certainconditions, the break contacts F3 and F5 are bypassed through breakcontacts S4 of the stop control relay.

When the elevator car is conditioned to run, the first timing relay 1BTis energized through the running relay. The relay 'lilT has a time delayin drop out which is provided in any suitable manner. For example, inFig. 1 a resistor R6 is connected across the coil of the relay for thepurpose of delaying drop out thereof.

Break contacts M1 of the running relay control the energization of asecond timing relay T. This relay also has a time delay in drop outwhich is provided in any suitable manner as by connection of a resistorR7 across the coil of the relay.

The auxiliary relay A may be energized from the buses L4 and L5 throughbreak contacts I IT! The third timing relay T is energized from thebuses L4 and L5 through the make contacts A4 6 of the auxiliaryirelayand the make contacts MlO of the running relay. The third timing relayhas a time delay in drop out which is provided in any suitable manner asby connection of a resistor R8 across the coil of the relay.

It will be recalled that the adjustable resistors RI and R4 are adjustedin accordance with a function of the loading of the motor IT. Thisfunction is determined by apparatus which includes three transformers25, 26 and 21. The transformer 25 has a primary winding connected acrossa resistor R! which is inserted in the bus LA. Consequently, thesecondary winding of the transformer has an output voltage El whichrepresents the current supplied to the phase winding IlA from the busLA.

The transformer 26 has a primary winding connected for energization bythe phase voltage E which is applied to the phase winding l'lA of themotor. (Conveniently, the voltage E may be applied to the phase windingHA and one or more of the resistors RA, RB or RC as shown). Thesecondary winding of the transformer 26 has a resistor RIB connectedthereacross.

across a resistor RI adjustable tap 29 associated therewith to providean adjustable voltage E3 which is dependent on the phase voltageappearing across the buses LB and LC.

By inspection of Fig. 1, it will be observed that the three voltages El,E2 and E3 are combined vectorially in series. The resultant is appliedthrough a rectifier 30 across an output resistor RIZ. A capacitor 3i isconnected across the output resistor R12 for the purpose of bypassingany alternating component of the energization of the resistor.

The nature of the output appearing across the resistor RI 2 may beunderstood from a considera tion of the vector diagram illustrated inFig. 1C. The phase voltage appearing across the phase winding l'lA ofthe motor I1 is represented in Fig. 1C by a vector E which issubstantially constant in magnitude. The output voltage El of thetransformer-25 is represented in Fig. 10 by a vector El which lags thereference voltage -E. It will be recalled that the voltage E l varies inaccordance with the phase current supplied to the phase winding HA ofthe motor.

The voltage El may be divided into two vector ponent EQ. Consequently,the resultant of the outputs of the transformers 25 and 2'! isrepresented by the vector component EP and this component represents therea1 power supplied to the motor.

The voltage E2. isderived from the transformer 7 26. The voltagetEZhasa. phas nelativev to. the vector 'EP and :a -magnitudennihich1maywbezadjusted to control the magnitude of theresultant output.

It is conventionalpractice in the elevator field to provide acounterweight 'l twhichbalances. the weight of the elevatorrcar 110 plus40% 9f the rated load capacity of athegelevator car. .For this reason,the elevator motor 11 :1 requires maximum power when carrying aiull loadin the up direc- .tion. For an overhaulingload, the motor l1 .gencratespower and the voltage E consequently swings substantially 180 in phaserelat'meto the voltage E2.

In the preferred embodiment of. the invention 1 the voltage E2compensates ;for :ahreeenerative value of the voltage vEP. the phase andmagnitude of the voltage EZaresoadjustedthat if the elevator car ismoving .down with a full load (i. e. an overhauling load) the resultantvoltage appearing across theresistor R12 is substantially zero. Withthis adjustment, if, the elevator car is moving .up with ;a fullload-the voltages E2 and EP are fin phase and .aJna-Ximum voltageappears across the ;;resistor Hit.

The output appearing across the 'resistor R12 is employed for.controllingthe adjustment of the resistors RI and B4. In a preierredembodiment of the invention, the output appearing across the resistorR|2 controls the position of a stepping switch which in turn controlsthe adjustment of the resistors fRl and as.

The stepping switch STP is of conventional .construction and may 'be.underetoodyirom. a consideration of Fig. 1B. The stepping switchincludes a shaft 35 having four double-ended wipers or contact arms 35A,35B, 35C and 35D secured thereto. The wiper 35A is employed foradjusting the efiective resistance value of the resistor RI. The wiper35B is employed for adjusting the effective resistance value of theresistor R4. The wiper 35C duringsuccessivestepping thereof successivelyengages contacts arranged in a semicircular bank. Onlyoneofthesecontacts 35E actually is employed for resetting purposes. The wiper .35Dis employed .for .controlling the effective resistance value of aresistor RM.

The shaft 35 also has secured thereto aratchet wheel 3515. This ratchetwheel is successively stepped in the direction of the arrowby-reciprocation-of a pawl 35G. When the coil'of thestepping switch STPis energized, an armature associated therewith lifts the pawl 35(3- andsimultaneously opens the break contactsSTPl. Opening of thecontacts STPIis employed .for deenergizing the coil of thestepping switch and :thepawl thereafter drops under the influence of gravity or preferably aspring (not shown) to advance the ratchet wheel .for an :angulardistance equivalent to one step. Such operation of a stepping switch iswell known in theart. The number of steps required to rotate :oneuo'fthe wiper ends across its associated resistor maybo the specificapplication. As an selected to suit example, twenty steps have beenfound adequate for someelevator applications of thetype hereindiscussed.

As shown 'in Fig. 1-, the coil of the stepping switch STP-is energizedfrom a secondary winding of a transformer thunder the control of anelectrical discharge device lii, the break contacts STPI and themakecontacts LUZ and 112132 The electrical discharge device 3'7 may beof any suit- .able type wherein the :output current thereof may becontrolled in in conductive condition,

from one terminal the transformer 36 a suitable manner. Iii-the specificembodiment of Fig. the -.electrical dis.- charge device takes the formof an electronic tube having a cathode 31A, a first grid or'con- .trolelectrode 313, a second grid or control electrode 31C and an anode 319.When the tube an energizing circuit for the coil of the stepping s tchmay be traced of the secondary winding .of through the contacts LD2,LUZ, STPI, the coil of the stepping switchSTP, the anode 31D, thecathode -3iA to the remaining terminal of the secondary'winding. Theprimary winding of the transformer 36 is energized from, a suitablesource of alternating current which may, for example, operate at theconventional power frequency of 60 cyclesper second.

the type designation Although the tube may be of the high vacuum type,a. thyratron tube such .as one sold under 2050 is considered to be verysatisfactory.

In-order to improve the operation of the stepping switch a rectifier 33may be connectedacross the coil, of the switch or preferably across thecoil and the contacts STPi as shown. This rec- "tifierpermits current toflow therethroughin the direction of the arrow. 'Iildesired a capacitorCl and aresistor are may be connected across the contacts STE todecrease arcing thereon The rectifiers employed in Fig. .1 may be oianysuitable type, but preferably are ofthedry-type such as those known ascopper oxide or selenium rectifiers.

13:18 is connected to resistor R15 and the .cated between the two Byinspection of Fig. 1 it will be observed that the resistors El i andRi'i are connected in series across a source of direct currentrepresented by a positive bus Li and a negative bus L6. The positive busalso is connected to the cathode 31A of the discharge device.Consequently, when the stepping switch is in reset condition, the second:grid 33.0 is maintained negative relative to the cathode 33A to preventoccurrence of a discharge .be'tween thecathode and anode of thedischarge device. A filter capacitor is connected between the first grid37B and the cathode, anda filter capacitor 11,

"3113 and th cathode a resistor R20, the the-resistor RI4,-andtheresistor R I] to metathis connected between the wiper 35Dandthe positive bus Ll.

. When thestepping switch is to step to a position corresponding to theloading of the motor 1], the 'break contacts SI and S3 open. Opening ofthe contacts S3 removes the negative bias applied to the second gridt'iC. The ,secondgrid 310 now is connected to the cathode only througharesistor R l 8.

The voltage appearing between the first grid 3M. now depends on thedifference between the voltage derived from the voltage dividerrepresented by the resistors RM and RH, and the voltage derived from theresistor R12. The biasing circuit may be traced from the first grid 3'iBthrough the resistor Hi6, resistor R1 2, the wiper 35D,

stepping switch S'I'P.

As the stepping switch operates, the wiper 35D moves in a clockwisedirection as viewed in Fig. l to increase the grid voltage derived fromthe voltage divider represented by the resistors RM and tinues until thegrid voltage derived from the voltage divider substantially balances thevoltage appearing across the resistor RI2. The position of the steppingswitch then corresponds to switch is to be reset, the break contacts SIand S3 of the stop control rethe contacts SI connects contact 35E.

Because of the connection of the first grid 3713 to the cathode, thedischarge device 31 again A complete operation of the elevator systemnow will be set forth.

Initially, it will be assumed that the elevator car ID is located at thelower terminal floor and that the stepping switch is in its resetcondition represented by the dotted line positions of the wiper arms inFig. 1. Under the assumed condi tions, break contacts Fl and F2 of theinductor relay are closed and the up stopping relay LU and the downstopping relay LD are energized and, picked up.

The car attendant now operates his car switch CS to engage the contactCS3 and complete the following circuit: L4, CS, CS3, U, LUI, 22, M, L5.As a result of its energization, closes its make contacts car switch CS.

At the same time energization of the running relay M re ults in closureof the make contacts MI and M2 to'energize the motor Closure of makecontacts M4 has no immediate effect on the operation of the system,Closure of make in the energizing circuit for the brake coil. Thisreduces the current flowing through the brake coil to a value merelysuflicient to maintain the brake in released condition.

Returning to the cheat of the energization and pick up of the runningrelay, it should be noted timing relay HIT. This relay closes its makecontacts 'IOTI without immediately affecting the operation of thesystem.

Opening of the break contacts M! deenergizes the second timing relay HTand this relay now starts to time out. Contacts M8 and M 10 close andbreak contacts M9 open without immediately affecting the operation ofthe system.

Upon expiration of the time required for the relay II T to drop out,this relay closes its break contacts H T l to complete through theclosed contact M8 an energizing circuit for the auxiliary relay A.

As a result of its energization, the auxiliary relay A closes its makecontacts Al and A2 to shunt the resistors RA, RB and RC. Such shuntingapplies full energization to the motor I! and conditions the motor forfull speed operation of the elevator car in the up direction. Theauxiliary relay also closes its make contacts A3 to energize the primarywinding of the transformer 21. A Voltage now appears across theresistors RIZ which depends on the loading of the motor l1.

Closure of the make contacts A4 completes through the closed makecontacts M H) an energizing circuit for the third timing relay T. Therelay T thereupon closes its make contacts TI to establish a holdingcircuit for the auxiliary relay A.

Let it be assumed tendant desires to st A suitable distance that theelevator car atp the car at the third floor.

tacts CS2. are closed, the stop control relay S is energized as a resultof such centering of the car switch.

The stop control relay opens its break contacts S to apply between thefirst grid 37B and the cathode 37A of the discharge device a voltagedependent on the diiference between that apby the resistors RI 4 and RH.break contacts bias from the second grid 31C.

The parameters of the system are assumed to be the up direction anoverhauling load having a smaller magnitude is applied to the elevatormotor and voltage appears across the resistor RIZ. For increases in theload carried by the apogee;

1'1 up-traveling elevator car the voltage across the resistor R12 alsoincreases.

It will be assumed that the rip-traveling elevator car IE3 is so loadedthat a voltage appears across the resistor R52 requiring stepping cf thestepping switch from the zero position represented by the dotted linepositions of the wipers to the position represented by the fulllinepositions of the wipers in Fig. 1. Under these conditions, a positivebias is applied to the first grid 31B and the discharge device 31conducts to energize the coil of the stepping switch. The steppingswitch now steps until the wiper 35D collects a sufhcient voltage fromthe associated voltage divider to balance substantially the voltageappearing across the resistor R12. The'stepping switch then'remains inthe position which is determined by the loading of the motor H.

The pick up of thestop control relay is also accompanied by closure ofthe make contacts S2 to energize the inductor relay F. However, suchenergization alone is insufiicient to pickup any or" the contacts oftheinductor relay. It will be recalled that in addition to'energizationof the coil of the inductor relay, .each of the inductor relay contactsmust be adjacent one or its associated inductor platesbefore suchcontacts can open. Opening of the break contacts S hasno immediateeffect onthe system operation.

When the elevator oar reaches apredetermined distance in advance of thethird floor-which may be of the order of 15 inches, the contacts F3 oithe inductor .relay reachthe up inductor plate for the third floor and'these'contacts thereupon open to deenergize the brake relay BR.

Deenergization of the .brakerelay results in openingof themake contactsBR! tointroduce the resistor R3 n the energizing circuit for the brakecoil .13. The resulting decrease'in energization of .the brake ooil'Binitiatesa decay in the magnetic flux of'the "brakecoil. .It will beassumed that 'such'decay'does not result in application of thebrake shoe2| to the drum 2%.

During continued motion 'of the elevator car, the contacts F! of theinductor relay plate reach the inductor plate for the third floor andopen to deenergize the up stopping relay LU. This may occur at asuitable distance from the third floor which may for example be of theorder of 9 inches for a slow speedelevatorcar.

The'up stopping relay LU .opensLthe-make contacts LUZ to preventmovement of the stepping switch during the stopping .operation. Inaddition, contacts LU! open to deenergize the up switch U and therunning. relay M. The running relay M opens its make contacts MI and M2to deenergize the elevator motor I]. In addition, the make contacts M3open to deenergize the brake coil B.

The energy stored in thebrake coil B'now'discharges through'theresistor'R i and the "rectifier R5. The resistor Rd hasaresistance'value as'determined by-the position of the wiper 3513 whichis properly coordinated for the purpose of stopping the elevator'car l8accurately at the third floor regardless of the magnitude of the loadcarried thereby. 'In the reset position of the wiper 3513 the resistorRd has a maximum efiective value. stepping switch which followed thepick up of the stop control relay S-decreased the effective resistanceto a value determined by the car loading. Opening oi1the make contactsMdand M5 has no immediate effect on the operation of the system.

However, the stepping of the F The running relay also opens its makecontacts M6 to deenergize the first timing relay 'iilTand this relay nowstarts to time out. Closure of break contacts Ml energizes the secondtiming relay liT-and the relay opens its break contacts HT! withoutimmediately afiecting the operation of the system. Opening of makecontacts M8 also has no immediate efiect on the operation of the system.

' The closure of the break contacts M9 of the running relay energizesthe dynamic braking relay DB through the closed contacts A4. The dynamicbraking relaycloses its make contacts DB1, DB2 and DB3 for the purposeof applying direct current to the phase winding 11C of the motor ll. Themagnitude of the resultant dynamic'braking is dependent on the positionof the wiper 35A and thisposition is coordinated with-the remainderof'the system to stop the elevator car accurately at the third floor.regardless of the loading thereof. In the reset position of the wiper35A the resistor BI is inefiective for limiting the energization of theprimary winding of the transformer Hi. However, the stepping of1thestepping switch'iollcwing-the pickup of the stop control relay Sprogressivelyincreasesthe efiectiveresistance of the resistor'Rluntil'it reaches a value representative of the car loading.

Returning to the running relay, this relay also opens its make contactsMID to .deenergize the third timing relay T and this relay now starts totimeout.

At the expiration of its time delay, the third timing relay T drops outto open its makecontacts Tl. This results in deenergization and drop outor" the auxiliary relay A. The relay .A opens its make contacts Al, A2and A3, but such opening does not immediately affect theoperationo'f'the system. Make contactsAd open to deenergize the dynamicbraking relay DB. This relay opensitsmake.contactsDBl, DB2 and-DB3 toterminate the supply-ofdirect current to .the motor I1.

Upon expiration of its time delay the relay 'ifii'I drops out .to openits contacts 'ESTJ. This results in deenergizationof the stop controlrelay S. The control relay closes its break contacts S! to connect thefirst grid 3130f thedischarge device to the cathode through the resistorRIG. Contacts S3 close, but have no immediate effect on the cperationofthe system. Closure of contacts .St has T-IlO immediate effect on theoperation of the system.

Dropout of the stop control relay also I results in opening ofthemakecontacts S2 to deenergize the inductorrelay F. This relay thereuponrecloses itsbreak-contacts El and F3. Closure of the contacts F3 has noimmediate eiiect on the operation of the system. Closure ofthe-contactsFl results in-energization of the up-stopping relayLU.

The up stopping 'relay'closes its make contacts LU; without immediatelyaffecting the operation of the system. "However closureoimake contactsLUZ completes an'energizing circuit for the stepping relay. lt'willberecalledthat at the time of such closure thefirst grid tlBis'connectedto the cathode through the-resistor EH6 and the contacts SI. At the sametime, the secon'd'grid BECis connectedto the cathode through theyresistorRlt. .Under these conditions, "the discharge device 331conducts and "the stepping .switch stepsruntil'rthe wiper .3ECsengageszthecontact 35E, :iSuch engagement'places arnegative tacts CS1and complete the following circuit: [4, CS, CSI, D, LDI, 23, M, L5. Thedown switch D closes its make contacts Di and D2 to pretacts D3 close toprepare the brake B for ener- Make contacts D4 close to establish abypass around the car switch.

The running relay M operates in the manner previously described for uptravel of the elevator car. However, since the closure of contacts DIand D2 conditions the system for down travel, it follows that theelevator car now moves away from the third iloor in the down direction.

As the elevator car nears the second floor, the elevator car attendantcenters his car switch CS to complete an energizing circuit for the stopcontrol relay S. This relay operates in the manner previously discussedto energize the inductor relay and to initiate a stepping operation ofthe stepping switch for the purpose of adjusting the stepping switch inaccordance with the loading of the elevator motor.

When the elevator car reaches a distance such as 15 inches in advance ofthe third floor, the break contacts F4 of the inductor relay reach thedown inductor plate for the second floor and open to deenergize thebrake relay BR. Upon deenergization, the brake relay operates in the"manner previously described to decrease the energization of the brakecoil.

When the elevator car reaches a predetermined distance such as 9 inchesin advance of the second. floor, the contacts F2 of the inductor relayreach the down inductor plate for the second floor and open todeenergize the down stopping relay LD. The down stopping relay ID opensits make contacts LDI to deenergize the down switch D and the runningrelay M. In addition, the make contacts LDZ open to prevent operation ofthe stepping switch during the stopping operation.

The running relay M upon deenergization operates in the same mannerdiscussed for the stopping of the elevator car during up travel in orderto stop the elevator car accurately at the second floor. Upon thedeenergization the down switch D returns its contacts to the conditionsillustrated in Fig. 1.

With the assumed parameters it will be noted that when the elevator cartravels down with a full load the stepping switch is positioned at thebeginning of a stopping operation to apply maximum direct current to themotor, and to introduce the maximum efiective value of the resistor R4across the brake coil. Consequently, a substantial dynamic braking isavailable and the brake is rapidly applied. When the elevator cartravels up with a full load the stepping switch is positioned at thebeginning of a stepping operation to apply minimum direct current to themotor and to introduce a minimum effective value of the resistor R4across the brake coil. The variations in direct current or dynamicbraking and in the rate of application of the mechanical brake isproportioned to assure accurate landing of the elevator car at a floorregardless of the amount of load carried thereby.

Either the adjustment of the resistor R4 or the I predetermined pointdynamic braking may be omitted for some application for which a singleadjustment suffices. The dynamic braking is particularly desirable,

Although th invention has been described with reference to certainspecific embodiments thereof, numerous modifications falling within thespirit and scope of the invention are possible.

I claim as my invention:

1. In a system for controlling a movable body, a structure, a bodymovable relative to said structure, motive means for moving the bodyrelative comprising first stopping chanically braking said body foradjusting the each of said stopping means in accordance with the energyto be absorbed during a stopping operation of the body.

2. A system as claimed in claim 1 wherein the electric motor is aninduction motor, and the second stopping means is effectiv for applyingto the induction motor windings direct current having a magnitude whichVaries as a function of the energy to be absorbed during a stoppingoperation of the body.

3. In a system for controlling a movable body, a structure, a bodymovable relative to ture, means for moving the body relative to thestructure, and. control means for controlling movement of the body, saidcontrol means comprising first stopping means operable for mechanicallybraking said body as it approaches a at which it is to stop, secondstopping means operable for electrically braking said body as itapproaches the predetermined point, means for partially operating saidfirst stopping means as it approaches the point, and means responsive toenergy to be absorbed during a stopping operation of the body foroperating each of the stopping means to adjust the braking effortexerted by each of the stopping means in accordance with the energy tobe absorbed.

4. In a system for controlling a movable body, a structure, a bodymovable relative to the structure, motive means for moving the bodyrelative to the structure, and control means for controlling movement ofthe body, said control means comprising first stopping means operablefor mechanically braking said body as it approaches a predeterminedpoint at which it is to stop, second stopping means, operable forelectrically braking said body as it approaches said predeterminedpoint, means responsive to arrival of said body at a predeterminedposition in advance of said predetermined point for initiatingoperations of the first and second means, and means responsive to energyto be absorbed during a stopping operation of the body for adjusting thebraking effort exerted by each of th stopping means in accordance withsaid energy to stop the body accurate- 13 at said predetermined point.

5. In a system for controlling a movable body,

a structure, a body :reprcsenting "-a variableload movable relative 1 tothe structure, 'electromotive rneans ior moving the body 'relativetothestructure, andcontrol means for controlling. movement of th body,said control: means comprising first stopping means operableiiormechanically brak ing saidbody as it approaches apredetermined point ;atwhich it is torstop, second stopping means operable for supplying directcurrent .to saidbodyas it approaches saidpredetermined point, meansresponsiveto arrival of said body at apredetermined position in advanceof said predetermined; point iorinitiatingoperations of the first andsecond means, andmeans'responsive to th magnitude of said load. foradjusting the braking effortexerted'by'the first-stopping means and-forvaryingithemagmtude orthe direct current to stop thcabodyaccurately atsaid predetermined point.

6. In an elevator system,aistructure having a plurality of floors, an:elevator :car movable-with respect to the structureto serve the floors,means including an electricinotor for moving the elevator-car relativeto the iioors,'-amechanical brake operable for stopping the elevatorcarat any of saidfloors, auxiliary braking operable for conditioningtheelectric motor to act as a dynamio brake,initiating means operable apredetermined distance :fromeachof the floors for initiating a stoppingoperation oftheelevator car :as'it approachesa floor at which itis tostop, and adjusting vmeans responsive to the load on said elevator*oarior adjustingithebralrin'g effort exerted'by the mechanical-brakeand for adjusting thgbraking-"efiort exerted by thedynarnic brake tostop theelevator caraccurately at any of the floors for which a stoppingoperation is initiated.

"Z. An elevator system as claimed in claim 5 wherein the adjusting.meansis responsive to the power supplied tosaid motor for moving theelevator car.

8. An -elev-ator systemas claimed in claim 6 "wherein the motor 'isaninduction motor, and wherein auxiliary meanscomprises a source of directcurrent and connections for energizing the induction motor from saidsource to produce dynamic braking of theelevator car, said adjustingmeansbeing effective'for adjusting the magnitude-oi the direct currentsupplied to said induction motor.

9. An elevator system as claimed in claim '6 wherein the adjusting meanscomprises a stepping'switch, means for'stepping' the switch to apositioncorresponding to the elevator car load, and means responsivestepping switch for adjusting said braking efforts.

10. In an elevator-system, a structure having 'a plurality of'floors,an'elevator car movable with respect to'the structure to serve thefloors, means including an electric motor'for moving the elevator carrelative to the floors, a mechanical brake operable for stopping theelevator carat .aany of said floors, auxiliary braking means operablefor-conditioning the electric motor to act as .a dynamic brake,initiatingrneans operable when in efiective condition a predetermineddistance from each of the floors for initiating a stopping operationofthe elevator car as it approaches afioor at'which it is to stop, andaddusting means responsive when in efiective condi- --tionto the loadonsaidelevator car for adjust- "ing the brakingseffort exertediby. themechanical brake and for adjusting stheibraking eilortexierted :byrthedynamic brakeito stopthe elevator to the position of the F6 :caraccurately at :any or the 'IfiOOlS :for which a stepping operation isinitiated, and effcctuating means operable while the elevator car is inmoition'for'placing saidinitiating means and theadjustingmeans ineffective condition.

11. Ina system for controlling a movable body, a structura'abodyrepresenting a variable load movablerelative to the structure, meansincludinganelectric motor for moving the body relative to the structure,and control means for controlling movement :of the body, said controlmeans comprisingrmeans connectingthe electric motor'to provide dynamicbraking for the body, adjusting means for adjusting the magnitude of thedynamic'braking'efiort produced by the electricimoton'an'd meansresponsive to the load represented by saidbodyior operating theadjusting means to vary the dynamic braking effort in accordance with apredetermined pattern.

'12. In a system'for controlling ainiovable body, a structure, 'abody'representing a variable load movable relative .to the structure,means'including an electric motor for moving the'body relative to thestructure, and control means for controlling movement of the body, saidcontrol means :tcomprising braking means for braking said body,adjusting means for adjusting the braking effort of the braking means, astepping svvitchhaving amovable operating member connected to operatesaidadjusting means and'having stepping means operable when in effectivecondition for successively stepping the operating member to spacedpositions, and means for energizing the stepping switch in accordancewith the difference between a quantity representing Jsaid load and a'quantity representing the displacement ofxthe operating member from apredetermined position, whereby the stepping-switch operates theadjusting means to produce a braking erIort having a magnitude dependenton said load.

'13. In a systemfor controlling a movable body, a structure, a bodyrepresenting a variable load movable relative to the structure, meansincluding aelectric motor for moving the body relative to the structure,and control means for controlling movement of the body, said controlmeans comprising braking means for braking said body, adjusting meansfor adjusting the braking eilort of the braking means, a stepping switchhaving a movable operating member connected to operate said adjustingmeans and having stepping means operable when in effective condition forsuccessively stepping the operating member to spaced positions, andmeans for energizing the stepping switch in accordance with thedifference between a quantity representing said load and a quantityrepresenting the displacement oithe operating member from apredetermined position, whereby the stepping switch operates'theadjusting means to produce a braking effort having a magnitude dependenton said load, operating means operable for placing said stepping meansin efiective conditionand initiating means responsive to operation ofthe operating means forinitiating a braking operation of the brakingmeans upon arrival of the body at a predetermined distance from a pointat which the body is to be stopped, said adjusting means controlling thebraking effort in accord- ;ance with said variable load to stop saidbody substantiallyat said point.

1.1.4..In :a load-responsive ldevice, translating meansifor actuating avariableiload, ansoperat- :member, :stepping means operable when ineffective condition operating member to spaced positions, translataposition dependent on said load.

15. In a load-responsive means for actuating a variable load, anoperating a predetermined point at which it is to stop, means responsiveon said motive means.

18. In a system for controlling a movable body, a structure,

gardless of the load represented by the body. ALVIN O. LUND.

References Cited in the file of this patent UNITED STATES PATENTS NameErbe Number Date 2,427,771

Sept. 23, 1947

